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Q & A: Heating Up a Tennis Ball

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Most recent answer: 10/22/2007
For a science project i am doing tennis balls bounce and if temperature effects it. The bit about the bounce was good but i need to know how thermal diffusion works in it. Does the expansion of the rubber allow the molecules to escape easier or does the heat speed up the energy state of the air inside enough to allow them to escape quicker?
- Andrew Piper (age 13)
St Leos, Sidney, NSW, AUS
Andrew -

Good question. You're right that the air gradually leaks out by thermal diffusion. That's the little random motions that the molecules have. Since the hotter they are, the more of that motion they have, you're right that the balls should leak more at high temperature. I'm not sure, but I'd bet your right that the rubber also gets leakier when it's hotter, because its molecules shake more and make it easier for the air to go through.

Just to make sure no one misunderstands, the immediate change you see in bounciness when you change the temperature just comes from changing the air pressure inside the ball. When it's hotter, it has higher pressure. The changes from the air leaking out by thermal diffusion happen very gradually.

For information about how heating up / cooling off a ball works, check out the answer to the question .

-Tamara & Mike

(published on 10/22/2007)

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